1. Field of the Invention
The present invention relates to methods, apparatus and software for maintaining continuing existence of a next-in-line protecting device (NPD) in an IEEE 802.22.1 system.
2. Description of the Related Art
The present invention incorporates by reference the Institute of Electrical and Electronics Engineers (IEEE) 802.22.1 Standard for Information technology: “Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 22.1: Enhanced Protection for Low-Power, Licensed Devices Operating in Television Broadcast Bands”. 
IEEE 802.22.1 defines a beacon network that offers enhanced protection for low power, licensed devices, such as wireless microphones, operating in television broadcast bands. The devices being protected are devices licensed as secondary under Title 47, Part 74, Subpart H in the U.S. Code of Federal Regulations, and equivalent devices in other regulatory domains.
The beacon network is constructed with three kinds of protecting devices: primary protecting device (PPD), secondary protecting device (SPD), and next-in-line protecting device (NPD). The PPD is a device that uses periodic beacons to protect its corresponding licensed device. The SPD is a device that shares the responsibility of protecting its corresponding licensed device with the PPD. An SPD occasionally sends beacons for the purpose of communicating with the PPD. The NPD is an SPD that will become a PPD in the event that the already existing PPD stops transmitting periodic beacon frames. That is, the PPD aggregates information from SPDs, periodically transmits beacon message, and provides primary beaconing functionality. When the PPD disappears, ideally the NPD shall promote itself as PPD. If both PPD and NPD disappear without warning, then a certain SPD will promote itself as the new PPD.
The contemporary NPD design is not complete. It is true that both PPD and SPDs could provide an indication after the NPD disappears for a certain time, but, if no SPD transmits any message to PPD, the PPD will not be able to promote any SPD as the new NPD. Consequently, the whole functionality of NPD is seriously weakened.